全文获取类型
收费全文 | 1624篇 |
免费 | 74篇 |
国内免费 | 25篇 |
专业分类
化学 | 1018篇 |
晶体学 | 4篇 |
力学 | 87篇 |
数学 | 257篇 |
物理学 | 357篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 55篇 |
2021年 | 42篇 |
2020年 | 78篇 |
2019年 | 53篇 |
2018年 | 56篇 |
2017年 | 46篇 |
2016年 | 102篇 |
2015年 | 82篇 |
2014年 | 101篇 |
2013年 | 134篇 |
2012年 | 142篇 |
2011年 | 152篇 |
2010年 | 105篇 |
2009年 | 70篇 |
2008年 | 62篇 |
2007年 | 76篇 |
2006年 | 73篇 |
2005年 | 45篇 |
2004年 | 50篇 |
2003年 | 37篇 |
2002年 | 36篇 |
2001年 | 20篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1930年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有1723条查询结果,搜索用时 0 毫秒
131.
Gas sensing is one of the most promising applications for graphene. Using molecular dynamics simulation method, adsorption isotherm of xenon (Xe) gas on defected and perfect graphene is studied in order to investigate sensing properties of graphene for Xe gas. In this method, first generation of Brenner many-body potential is used to simulate the interaction of carbon–carbon (C) atoms in graphene, and Lennard–Jones two-body potential is used to simulate interaction of Xe–Xe and Xe–C atoms. In the simulated systems, adsorption coverage, radial distribution function, heat of adsorption, binding energy and specific heat capacity at constant volume are calculated for several temperatures between 90 K and 130 K, and various pressures. It was found that both of the defected and perfect graphene could be introduced as very good candidates for adsorption of Xe gas. 相似文献
132.
133.
Maliheh Khatibi Moghaddam Amir Reza Attari Mir Mojtaba Mirsalehi 《Photonics and Nanostructures》2010,8(1):47-53
We investigate a photonic crystal (PC) waveguide coupler which is formed by two closely spaced linear waveguides in a two-dimensional triangular lattice of air holes. Our study shows that shifting one row of the air holes between the waveguides affects the dispersion curves of the guided modes and if the triangular lattice of air holes between the waveguides is replaced by a rectangular lattice, this modification results in an ultra-short coupling structure with coupling length less than 3a, where a is the lattice constant. Also, we investigate the effect of changing the radii of air holes that are adjacent to or between the waveguides on the coupling length and show that increasing the radius of air holes between the waveguides decreases the coupling length. We analyze the output spectrum of an ultra-short channel drop filter designed based on this structure. 相似文献
134.
135.
Dganit Amitai Amir Averbuch Moshe Israeli Samuel Itzikowitz 《Numerical Algorithms》1996,12(1):159-192
In achieving significant speed-up on parallel machines, a major obstacle is the overhead associated with synchronizing the concurrent processes. This paper presents high-orderparallel asynchronous schemes, which are schemes that are specifically designed to minimize the associated synchronization overhead of a parallel machine in solving parabolic PDEs. They are asynchronous in the sense that each processor is allowed to advance at its own speed. Thus, these schemes are suitable for single (or multi) user shared memory or (message passing) MIMD multiprocessors. Our approach is demonstrated for the solution of the multidimensional heat equation, of which we present a spatial second-order Parametric Asynchronous Finite-Difference (PAFD) scheme. The well-known synchronous schemes are obtained as its special cases. This is a generalization and expansion of the results in [5] and [7]. The consistency, stability and convergence of this scheme are investigated in detail. Numerical tests show that although PAFD provides the desired order of accuracy, its efficiency is inadequate when performed on each grid point.In an alternative approach that uses domain decomposition, the problem domain is divided among the processors. Each processor computes its subdomain mostly independently, while the PAFD scheme provides the solutions at the subdomains' boundaries. We use high-order finite-difference implicit scheme within each subdomain and determine the values at subdomains' boundaries by the PAFD scheme. Moreover, in order to allow larger time-step, we use remote neighbors' values rather than those of the immediate neighbors. Numerical tests show that this approach provides high efficiency and in the case which uses remote neighbors' values an almost linear speedup is achieved. Schemes similar to the PAFD can be developed for other types of equations [3].This research was supported by the fund for promotion of research at the Technion. 相似文献
136.
Light is shown to exhibit critical and tricritical behavior in passively mode-locked lasers with externally injected pulses. It is a first and unique example of critical phenomena in a one-dimensional many-body light-mode system. The phase diagrams consist of regimes with continuous wave, driven parapulses, spontaneous pulses via mode condensation, and heterogeneous pulses, separated by phase transition lines that terminate with critical or tricritical points. Enhanced non-Gaussian fluctuations and collective dynamics are present at the critical and tricritical points, showing a mode system analog of the critical opalescence phenomenon. The critical exponents are calculated and shown to comply with the mean field theory, which is rigorous in the light system. 相似文献
137.
Efficient enantioselective Cu-catalyzed allylic alkylations of aromatic and aliphatic allylic phosphates bearing di- and trisubstituted olefins are disclosed. Enantioselective C-C bond forming reactions are promoted in the presence of 10 mol % readily available chiral amino acid-based ligand (5 steps, 40% overall yield synthesis) and 5 mol % (CuOTf)2 x C6H6. Reactions deliver tertiary and quaternary stereogenic carbon centers regioselectively and in 78-96% ee. Data regarding the effect of variations in ligand structure on the efficiency and enantioselectivity of the alkylation process, as well as a mechanistic working model, are presented. The suggested model involves a dual role for the chiral Cu complex: association of the Cu(I) center to the olefin is facilitated by a two-point binding between the carbonyl of the ligand's amide terminus and the P=O of the substrate. 相似文献
138.
Shapira B Karton A Aronzon D Frydman L 《Journal of the American Chemical Society》2004,126(4):1262-1265
We have recently proposed and demonstrated an approach that enables the acquisition of multidimensional nuclear magnetic resonance (NMR) spectra within a single scan. A promising application opened up by this new accelerated form of data acquisition concerns the possibility of monitoring in real time the chemical nature of analytes subject to a continuous flow. The present paper illustrates such potential, with the real-time acquisition of a series of 2D 1H NMR spectra arising from a mixture of compounds subject to a continuous liquid chromatography (LC) separation. This real-time 2D NMR identification of chemicals eluted minutes apart under usual LC-NMR conditions differs from the way in which LC-2D NMR has hitherto been carried out, which relies on stopped-flow modes of operations whereby fractions are first collected and then subject to individual, aliquot-by-aliquot analyses. The real-time LC-2D NMR experiment hereby introduced can be implemented in a straightforward manner using modern commercial LC-NMR hardware, thus opening up immediate possibilities in high-throughput characterizations of complex molecules. 相似文献
139.
Fluorescent optical imaging of tumors deep within tissue depends on specific binding of antibodies to the tumors' surface markers. These fluorescent antibodies propagating in the vicinity of the tumor can be attached to and (or) diffused away from it. We illustrate application of a new tool, based on the random-walk theory in turbid media, for extracting the pharmacokinetics of these fluorescent antibodies by data deconvolution, excluding the effect of upper turbid tissue layers. 相似文献
140.
Volinsky R Kolusheva S Berman A Jelinek R 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):11084-11091
Lipid interactions and cooperative assembly properties are fundamental determinants for the action of antimicrobial membrane-active peptides. Here we analyze the interactions and aggregation properties of alamethicin, an antimicrobial pore-forming peptide, with films formed at the air/water interface. Surface-area/pressure isotherms, Brewster angle microscopy, and fluorescence-confocal microscopy provided detailed information on the morphologies and structural properties of the peptide and its effect on the film components. The pressure-area analysis and microscopy experiments facilitated unprecedented visualization of the structural consequences of alamethicin association at the air/water interface, with pure phospholipid films, and within mixed phospholipid/polydiacetylene (PDA) films. The analysis exposed the kinetic features and the interplay between the peptide aggregates and film constituents. In particular, the results demonstrate the use of phospholipid/PDA film assemblies for studying membrane-peptide association and interactions within two-dimensional films. 相似文献